Question

X-y = 4
-2x +y=-7
nilai x-3y adalah
a.-3
b.3
c.4
d.-6

Answer 1

⇒  x -  y = 4
     -2x + y= -7
     ---------------(+)
     -x = -3
       x = 3
⇒x - y = 4
   3 - y = 4
     y = -1
⇒x - 3y = 3 - 3(-1) = 6

Answer 2

x-y = 4
y = x-4

-2x+y = -7
-2x+x-4 = -7
-x-4 = -7
-x = -7+4
-x = -3
x = 3
y = x-4
y = 3-4
y = -1

x-3y = 3-3(-1)
        = 3+3
        = 6